Purpose: We assessed the accuracy of communication between doctors and patients by evaluating the consistency between patient perception of cancer stage and the medical records, and analyzed the most influential factors of incongruence among cancer patients at 10 cancer centers across Korea. Methods: Information was gathered from cancer patients at the National Cancer Center and nine regional cancer centers located in every province of Korea between 1 July 2008 and 31 August 2008. Data were analyzed using Pearson's χ2 test and multivariate logistic regression analysis. Results: The stages of cancer reported by the 1,854 patients showed a low degree of congruence with the stages given in medical records (k = 0.35, P<0.001). Only 57.1% of the patients had accurate knowledge of their cancer stage. In total, 18.5% underestimated their stage of disease, and the more advanced the cancer stage, the more likely they were to underestimate it, in order of local (14.2%), regional (23.7%), and distant (51.6%). Logistic regression analysis showed that congruence was lower in patients with cervical cancer (odds ratio [OR] = 0.51, 95% confidence interval [CI] = 0.30–0.87), recurrence (OR = 0.64, 95% CI = 0.50–0.83), and treatment at the National Cancer Center (OR = 0.53, 95% CI = 0.39–0.72). Conclusion: There are knowledge gaps between patients' perceived and actual stage of cancer. Patients with cervical cancer, recurrence, and who received treatment at a regional cancer center showed less understanding of their cancer stage.